This invention relates to processes for producing alkyd resins using polyester resins which have been recovered from waste materials such as disused PET bottles and regenerated.
Heretofore, use of terephthalic acid as the dibasic acid component, which is one of the starting materials of alkyd resins, was more costly than using phthalic acid or phthalic anhydride and the resulting resin was apt to become turbid or develop occurrence of foreign matters. Hence, normally terephthalic acid is not used for alkyd resin production or, if used, in only minor amount. On the other hand, recently disposal of waste is becoming a serious issue and utilization of disused PET bottles by recycling is under study.
A production method of alkyd resins using polyester resins which have been recovered from waste materials such as disused PET bottles and regenerated is described in, for example, Hei 11 (1999)-228733A-JP. Said method comprises subjecting recovered polyester resin and an alkyd resin oligomer having a molecular weight not higher than 5,000 and containing hydroxyl groups to depolymerization and transesterification. However, this method is subject to a number of problems such that it requires advance synthesis of the alkyd resin oligomer, requires many hours for the depolymerization and filtration of ultimately obtained alkyd resin causes occurrence of large amount of filtration residue, because the amount of the alcohol component in the occasion of depolymerization is too low to sufficiently depolymerize the recovered polyester resin.
The object of the present invention is to provide processes for producing transparent alkyd resins which are substantially free of foreign matters and filtration residue within a short time, using the polyester resins which have been recovered from waste materials and regenerated.
We have engaged in concentrative studies with the view to accomplish the above object and now discovered that the object could be fulfilled by conducting depolymerization of said recovered and regenerated polyester resin as dissolved in a mixture or reaction mixture of an alcohol mixture of tetra- or higher hydric alcohol and tri- or lower polyhydric alcohol, or an alcohol component comprising tetra- or higher alcohol, with an oil and fat and/or a fatty acid; and then conducting an esterification reaction by adding a polybasic acid component and if necessary a fatty acid component to the system and come to complete the present invention.
Thus, according to an embodiment of the invention, a process of producing an alkyd resin having an oil length of 30-70% is provided, which is characterized by comprising dissolving a polyester resin, whose chief starting material is terephthalic acid and which has been recovered from waste materials and regenerated, in an alcohol mixture of tetra- or higher hydric alcohol and tri- or lower polyhydric alcohol at a weight ratio as the former/the latter within a range of 0.2-50, depolymerizing the polyester resin in the presence of a depolymerization catalyst, and then adding to the system a polybasic acid component and a fatty acid component to subject them to an esterification reaction, the polyester resin being used in an amount of 5-40% by weight based on the total weight of the polyester resin, the alcohol mixture, the polybasic acid component and the fatty acid component (this process is hereafter referred to as xe2x80x9cthe first processxe2x80x9d).
According to another embodiment of the present invention, another process of producing an alkyd resin having an oil length of 30-70% is provided, which is characterized by dissolving a polyester resin, whose chief starting material is terephthalic acid and which has been recovered from waste material and regenerated, in a mixture or reaction product of an alcohol component containing tri- or lower polyhydric alcohol and tetra- or higher hydric alcohol at a weight ratio of the former/the latter within a range of 0-20, with an oil and fat and/or a fatty acid, depolymerizing the polyester resin in the presence of a depolymerization catalyst, and then adding a polybasic acid component to the system to subject them to an esterification reaction, the polyester resin being used in an amount of 5-40% by weight based on the total weight of the polyester resin, the alcohol component, the oil and fat and/or the fatty acid and the polybasic acid component (xe2x80x9cthe second processxe2x80x9d).
According to the invention, furthermore, paint compositions containing the alkyd resins which are produced by the above first or second process are provided.
Hereinafter the first and second processes of the invention are explained in further details.
Those polyester resins made chiefly from terephthalic acid, which have been recovered from waste materials and regenerated, and which are used in the first and second processes of this invention (hereafter the polyester resins may be abbreviated as xe2x80x9cregenerated PESxe2x80x9d) include polyethylene terephthalate (e.g., PET bottles) which are recovered for recycling of resources, industrial waste polyethylene terephthalate, and polyester resins regenerated from the wastes occurring in the course of production of polyester products (film, fibres, automobile parts, electric and electronic parts, etc.) such as polyethylene terephthalate or polybutylene terephthalate made chiefly from terephthalic acid. In particular, recycled polyethylene terephthalate is suitable. The regenerated PES is normally used in the form of chips or pulverized product.
According to the first process of the invention, first such regenerated PES is dissolved in a mixture of a tetra- or higher hydric alcohol and a tri- or lower polyhydric alcohol, and its depolymerization is conducted in the presence of a depolymerization catalyst.
Examples of tetra- or higher hydric alcohols useful in said alcohol mixture include diglycerine, triglycerine, pentaerythritol, dipentaerythritol and sorbitol. Of those, pentaerythritol is particularly suitable because of favorable curing and drying property of the painted film of the paint compositions in which the resulting alkyd resin is used. Also examples of tri- or lower polyhydric alcohols include: trihydric alcohols such as trimethylolpropane, trimethylolethane and glycerine; and dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol and 1,4-dimethylolcyclohexane. Of those, glycerine, ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol are particularly suitable, from the standpoints of depolymerization ability as used in mixtures with said tetra- or higher hydric alcohols (e.g., pentaerythritol) and low-temperature dissolving ability of high temperature-melting tetra- or higher hydric alcohols.
In the alcohol mixture, blend ratio of the tetra- or higher hydric alcohol to the tri- or lower polyhydric alcohol is conveniently within a range of 0.2-50, preferably 0.5-35, inter alia, 1-20, in terms of weight ratio of the former/the latter.
The blend ratio of said regenerated PES to the alcohol mixture is within a range of 15/85-80/20, in particular, 20/80-70/30, inter alia, 20/80-60/40, in terms of a weight ratio of the former/latter.
On the other hand, in the second process of the invention, said regenerated PES is dissolved in a mixture of an alcohol. component containing a tetra- or higher hydric alcohol as exemplified in the above as the essential constituent and if necessary a tri- or lower polyhydric alcohol as above-exemplified, with an oil and fat and/or a fatty acid, or in an esterification reaction mixture thereof, and is depolymerized in the presence of a depolymerization catalyst. In this specification, the word xe2x80x9cesterificationxe2x80x9d is used in a sense covering both ordinary estirification reaction and ester- interchange reaction.
In the above alcohol component, convenient blend ratio of tri- or lower polyhydric alcohol to tetra- or higher hydric alcohol is, in terms of the former/the latter by weight, within a range of 0-20, preferably 0.02-10, inter alia, 0.05-5.
Examples of the oil and fat, i.e., triglycerides of fatty acids, and/or the fatty acids to be mixed with above alcohol component include the following: as oils and fats, soybean oil, safflower oil, linseed oil, tall oil, coconut oil, palm kernel oil, castor oil, dehydrated castor oil, fish oil and tung oil can be named. In particular, drying or semi-drying oils having iodine values of at least 100 are preferred, inter alia, soybean oil and tall oil are advantageous. As fatty acids, those of soybean oil, safflower oil, linseed oil, tall oil, coconut oil, palm kernel oil, castor oil, dehydrated castor oil, fish oil, and tung oil may be named. Of those fatty acids, those of drying oils or semi-drying oils having iodine values of at least 100, inter alia, those of soybean oil and tall oil, are preferred.
The blend ratio of the oil and fat, and/or the fatty acid with the alcohol component is such that the oil length of the resulting alkyd resin should range 30-70%, preferably 40-60%, for imparting adequate drying property and physical properties of the dry coated films of paint compositions in which the alkyd resin is blended.
In the second process of the invention wherein regenerated PES is mixed with, and dissolved in, an esterification reaction product of the alcohol component with oil and fat, and/or fatty acid, said esterification reaction product is provided by subjecting a mixture of the alcohol component with oil and fat, and/or fatty acid to an esterification reaction in advance. This esterification reaction can be conveniently carried out by any method known per se, in the presence of an esterification catalyst such as zinc acetate, litharge, dibutyltin oxide and the like.
Polyhydric alcohols which are normally solid, such as pentaerythritol, dissolve in the system upon said esterification reaction with fatty acid, to facilitate the dissolving and deploymerization of regenerated PES in the next step. Also advance blending of liquid oil and fat in said mixture enables stable progress of the esterification reaction between polyhydric alcohol and fatty acid.
The amount of regenerated PES to be blended in a mixture of the alcohol component and the oil and fat and/or the fatty acid, or an esterification reaction product of said mixture, is normally within a range of 15-80, in particular, 20-70, inter alia, 20-60, parts by weight, per 100 parts by weight of the sum of the regenerated PES, alcohol component, the oil and fat and/or the fatty acid. Here xe2x80x9cthe sum of the regenerated PES, alcohol component, the oil and fat and/or the fatty acidxe2x80x9d signifies, in case of blending the regenerated PES in the esterification product, the combined amount of the sum of the alcohol component and the oil and fat and/or the fatty acid, which are the starting materials of the esterification product, plus the regenerated PES.
As examples of depolymerization catalyst which is used for promoting depolymerization of regenerated PES in the first and second processes of the invention, monobutyltin hydroxide, dibutyltin oxide, monobutyltin-2-ethyl hexanoate, dibutyltin dilaurate, stannous oxide, tin acetate, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, antimony trioxide, tetrabutyl titanate and tetraisopropyl titanate maybe named. The use rate of the depolymerizaton catalyst in the first process is, per 100 weight parts of the total sum of the regenerated PES and alcohol mixture, conveniently within a range of normally 0.005-2, in particular, 0.05-2, weight parts; and in the second process of the invention, per 100 weight parts of the sum of the regenerated PES, the alcohol component, and the oil and fat and/or the fatty acid, it is normally conveniently within a range of 0.005-5, in particular, 0.05-5, weight parts.
In the first process of the invention, the depolymerization method of regenerated PES by dissolving it in an alcohol mixture is subject to no critical limitation, so long as the regenerated PES can be dissolved in the alcohol mixture and the depolymerization can be effected. For example, a method may be named in which a depolymerization catalyst is blended in an alcohol mixture which is heated to 80-250xc2x0 C., preferably 100-240xc2x0 C., and to which regenerated PES is added and together heated to cause its dissolution and depolymerizaton at, for example, 140-250xc2x0 C., preferably 150-240xc2x0 C.
According to the first process of the invention, after conducting the dissolution and depolymerization of the regenerated PES, a polybasic acid component and fatty acid component are added to the system to conduct an esterification reaction to form an alkyd resin. In said production of alkyd resin, coloring in the formed alkyd resin can be inhibited by adding to the depolymerization product of the regenerated PES a minor amount, e.g., 0.1-10 weight parts, of a phosphorus compound per 100 weight parts of said depolymerization product in advance. As examples of the phosphorus compound, phosphoric acid, phosphorous acid and hypophosphorous acid; and alkyl esters or phenyl esters of these acids (e.g., trimethyl phosphite, trimethyl phosphate, triphenyl phosphite and triphenyl phosphate) may be named.
As the polybasic acid component, those normally used as the acid component for forming alkyd resins can be similarly used. For example, dibasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, naphthalenedicarboxylic acid, 4,4xe2x80x2-biphenyldicarboxylic acid, diphenylmethane-4,4xe2x80x2-dicarboxylic acid, succinic acid, fumaric acid, adipic acid, sebacic acid and maleic anhydride; tri- and higher polybasic acids such as trimellitic anhydride, pyromellitic anhydride, trimesic acid and methylcyclohexenetricarboxylic acid; and C1-C6 (in particular, C1-C4) alkyl esters of those dibasic acids and tri- and higher polybasic acids can be named. Of those, dibasic acids and their C1-C6 (in particular, C1-C4) alkyl esters are preferred.
As the fatty acid component to be used in the alkyd resin production, fatty acid, oil and fat, and the like may be named. As fatty acid, for example, soybean oil fatty acid, safflower oil fatty acid, linseed oil fatty acid, tall oil fatty acid, coconut oil fatty acid, palm kernel oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, fish oil fatty acid and tung oil fatty acid may be named. As examples of useful oil and fat, esters of above fatty acids with glycerine can be named, such as soybean oil, safflower oil, linseed oil, tall oil, coconut oil, palm kernel oil, castor oil, dehydrated castor oil, fish oil and tung oil and the like. Of those fatty acid component, fatty acids of drying oils or semi-drying oils having iodine values of at least 100, inter alia, soybean oil fatty acid and tall oil fatty acid, are preferred.
The blend ratio of the above fatty acid component is such that the oil length of the resulting alkyd resin should range 30-70%, preferably 40-60%, for imparting adequate drying property and physical properties of the dry, coated films of paint compositions in which the alkyd resin is blended. For accomplishing this, generally preferred use ratio of the polyester resin is 5-40%, in particular, 10-35%, inter alia, 10-30%, by weight, based on the total weight of the polyester resin, alcohol mixture, polybasic acid component and the fatty acid component. It is also preferred to use the polybasic acid component and the fatty acid component at such ratios that the carboxyl equivalent numbers in the sum of the polybasic acid component and the fatty acid component per one hydroxyl equivalent in the alcohol mixture falls within a range of 0.8-1, in particular, 0.85-0.99, inter alia, 0.90-0.99, for obtaining favorable water resistance and physical properties of dry coating film formed by applying paint compositions containing said alkyd resin. Here the xe2x80x9ccarboxyl groups in the sum of polybasic acid component and the fatty acid componentxe2x80x9d is calculated, where the polybasic acid component is an ester of a polybasic acid, by hydrolyzing the ester and using the formed carboxyl groups.
The esterification reaction for obtaining alkyd resin following the first process of the present invention can be conducted under esterification reaction conditions known per se. For example, a system composed of a depolymerization product of a polyester resin with an alcohol mixture, which is obtained as above-explained, to which the polybasic acid component and fatty acid component are added, is kept at temperatures from about 110xc2x0 C. to about 260xc2x0 C., preferably from about 150xc2x0 C. to 250xc2x0 C., for about 3 to 10 hours in the presence of an esterification catalyst, to be dehydrated and condensed. As catalyst for the esterification reaction, those earlier named as examples of depolymerization catalyst can be used. The use rate of such esterification catalyst is normally conveniently within a range of 0.005-2% by weight, in particular, 0.05-2% by weight, to the above system.
In the second process of the invention, depolymerization can be effected by such methods as, for example, (1) mixing a mixture of the alcohol component, oil and fat and/or fatty acid with regenerated PES and dissolving the latter to effect the depolymerization, or (2) mixing an esterification reaction product from alcohol component, oil and fat, and/or fatty acid with regenerated PES, and dissolving the latter to carry out the depolymerization. The method (2) is more convenient, in respect of depolymerizability of regenerated PES.
Depolymerization conditions of regenerated PES are not subject to critical limitations, so long as they allow the depolymerization using a depolymerization catalyst. For example, a method comprising adding regenerated PES to a mixture of the alcohol component, oil and fat, and/or fatty acid, or an esterification reaction product of said mixture, said mixture or the reaction product thereof being heated to 80-250xc2x0 C., preferably 100-240xc2x0 C., and heating the system in the presence of a depolymerization catalyst to, e.g., 140-250xc2x0 C., preferably 150-240xc2x0 C., to effect dissolution and depolymerization.
According to the second process of the present invention., alkyd resin can be obtained, after dissolving and depolymerizing regenerated PES in the above-described manner, by adding to this depolymerization product a polybasic acid component similar to the one as was explained in respect of the first process of the present invention to cause esterification reaction thereof.
In said occasion, it is appropriate to use the regenerated PES in such an amount as will render the oil length of resultant alkyd resin within a range of 30-70%, preferably 40-60%, in respect of drying property and physical properties of coated film when made dry coated film. For this purpose, it is generally preferred to use regenerated PES in an amount of 5-40 weight percent, in particular, 10-35 weight percent, inter alia, 10-30 weight percent, based on the sum of the regenerated PES, alcohol component, oil and fat, and/or fatty acid, and polybasic acid component.
It is also convenient for waterproof property and physical properties of coated film when made dry coated film, to make the equivalent number of carboxyl group(s) in the polybasic acid component per equivalent of hydroxyl group in said alcohol component 0.5-1, in particular, 0.6-0.99, inter alia, 0.7-0.99. Here xe2x80x9ccarboxyl group(s) of polybasic acid componentxe2x80x9d signifies, where the polybasic acid component is an ester of polybasic acid, the carboxyl group(s) as converted by hydrolysis of said ester.
The esterification reaction for obtaining an alkyd resin following the second process of the present invention can be conducted under esterification reaction conditions known per se. For example, it can be conducted by maintaining a system formed by blending a polybasic acid with a dissolution and depolymerization product from regenerated PES, alcohol component, oil and fat, and/or fatty acid, at about 110xc2x0-about 260xc2x0 C., preferably about 150xc2x0-about 250xc2x0 C., in the presence of an esterification catalyst, for about 3-10 hours to cause dehydration and condensation. As the esterification catalyst, those earlier named as examples of depolymerization catalyst can be used. Suitable blend ratio of the esterification catalyst is normally 0.005-5 weight percent, in particular, 0.05-5 weight percent, to said system.
In the production of alkyd resin, coloration of formed alkyd resin can be inhibited by adding to the depolymerization product of regenerated PES, in advance of the esterification reaction, a minor amount, e.g., 0.1-10 weight parts per 100 weight parts of said product, of a phosphorus compound. As the phosphorus compound, for example, phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl esters or phenyl esters of these acids (e.g., trimethyl phosphite, trimethyl phosphate, triphenyl phosphite, triphenyl phosphate and the like) may be named.
In the above-described first and second processes, after termination of the esterification reaction, the alkyd resin is normally cooled and may be recovered as it is. Whereas, for improving filterability and handling workability, the resin may be diluted with organic solvent and recovered. The kind of organic solvent is not particularly limited, so long as it can dissolve the alkyd resin.
Those alkyd resins obtained by the first and second processes of the present invention are excellent in solubility in organic solvent, are soluble in even such weak solvent as mineral spirits although they contain terephthalic acid component, and are useful as resin binder in paint compositions. Recently overcoatability is attached greater importance and alkyd resins soluble in weak solvent are highly evaluated. The alkyd resins obtained by the processes of the present invention well meet this purpose.
Alkyd resins obtained by the processes of the invention preferably have oil length of 30-70%, in particular, 40-60%;
number-average molecular weight of 2,000-12,000, in particular, 2,500-10,000; hydroxyl value of 10-150 mgKOH/g, in particular, 15-130 mgKOH/g; and an acid value of 1-50 mgKOH/g, in particular, 3-20 mgKOH/g.
Of the alkyd resins obtained by the processes of the present invention, those in which drying oil fatty acids or semi-drying oil fatty acids are used as the fatty acid excel in oxidation-drying property and are conveniently used as resins for room temperature-curing type paints. Where they are used as resins for room temperature-curing type paints, the drying property can be still improved by concurrent use of metal compound dryers such as cobalt naphthenate, zirconium naphthenate, lead naphthenate and the like. The alkyd resins obtained by the processes of the present invention, in particular, those in which saturated fatty acids are used as the fatty acid, can be conveniently used as resins for thermosetting type paints, in combination with curing agents reactable with hydroxyl groups, such as amino resins like melamine resin, polyisocyanate compound, epoxy compound and the like. Paint compositions containing the alkyd resins obtained by the processes of the present invention can be prepared by methods known per se, provided that an alkyd resin of the invention is used as at least a part of the resin binder.